Automotive alternators are driven at widely varying speeds. Alternators of that type usually include a fan wheel to cool the alternator. It is usually seated on the alternator shaft, and may be coupled to the alternator shaft by a coupling which may include a ball bearing and a friction drive which provides for frictional engagement of the fan blade with the drive pulley of the alternator, but permits slipping of the fan blade with respect to the drive pulley of the alternator if the engine speed, and hence the speed of the alternator, rises above limits which would be detrimental to operation of the fan blade, or cause excessive noise or power consumption.
Speed-dependent or speed-limited fan blade couplings have been previously proposed; see, for example, German Patent Disclosure Document DE-OS No. 29 42 737 corresponding to U.S. Pat. No. 4,437,846, Ragaly, issued Mar. 20, 1984. In one such arrangement, two ball bearings are located on a single drive shaft for the alternator, one of the ball bearings journalling the drive shaft with respect to the alternator housing, the other ball bearing securing the fan blade on the alternator shaft. The ball bearing which is immediately adjacent the end bell or end plate of the alternator is axially irremovably secured to the generator shaft. The outer race of the ball bearing is coupled to the fan blade. The other ball bearing has its inner race axially slidably located on the shaft, and has its outer race positioned against a leaf spring which provides axial compressive force against the outer race of the first ball bearing. As the speed of the shaft increases, driven by a pulley which, for example, is coupled by a V-belt with the engine, the outer race of the ball bearing carrying the fan blade is carried along until the resistance torque of air flow which must be overcome by the fan wheel increases beyond the frictional torque set by the spring between the two ball bearings. As the speed of the shaft increases, the speed of the outer race of the ball bearing carrying the fan blade increases only slightly, or may remain constant or steady.
The foregoing construction is somewhat difficult to assemble, particularly under mass production conditions.